References in this specification to ‘pipelines’ cover conduits such as flowlines. Also, references to ‘milling’ include methods of cutting into a pipeline, for example using a drill bit, mill or an abrasive jet. References to E-line cover any cable, braided line or slick line that conveys a mechanical or electrical assembly to perform various operations or take measurements.
In oil and gas production and processing, pipelines are commonly used to transport fluids such as petroleum and gas, and can be used in both surface and sub sea applications. The pipelines can be used to connect any two locations, for example a pipeline can extend between a well head and a manifold, a manifold and a production facility or a production facility and a centralised storage facility.
Pipelines can become blocked during use, for example by hydrates, wax, scale or other undesirable components present in the fluid or by equipment, such as pigs, stuck in the pipeline. Many measures are known to prevent or reduce the chance of blockage formation. One common technique is the injection of chemicals into production wells and pipelines, the chemicals acting to inhibit blockage formation. However, such injection of chemicals is expensive and blockages can still form in some cases, particularly if a pipeline is shut down causing the fluid temperature to drop.
WO 2004/033850 discloses a flow assurance system which can be used to monitor the conditions inside a flowline, to minimise the risk of blockages forming or to perform cleaning operations inside the flowline if undesirable constituents begin to build up. The system includes an inner pipe disposed within an outer pipe (the flowline). One end of the inner pipe is connected at a production facility. The other end of the inner pipe can be open to the outer pipe, for example so as to deliver chemicals through the inner pipe to a desired point in the outer pipe. In another example, the inner pipe may form a closed circuit and a hot fluid such as hot sea water can be passed through the closed loop of the inner pipe so as to warm up the fluids in the outer pipe. In yet another example, a variety of tools can be attached to the end of the inner pipe. For example, a scraper can be attached to the end of the inner pipe and the inner pipe moved through the outer pipe so that the scraper mechanically cleans the walls of the outer pipe.
The inner pipe is preferably installed into the downstream end of the outer pipe from a platform. However, the inner pipe can also access the flowline at its upstream end or at any point along the flowline.
Pipelines can extend extremely long distances, and so it is desirable to be able to access a pipeline at a desired point along the pipeline, since a blockage can form at any point. There is therefore a need for a method of accessing specific points along a pipeline.
Methods of accessing a specific point in an existing pipeline in order to connect a new pipeline to the existing pipeline without depressurising the existing pipeline are known, and are commonly described as “hot tapping” methods. WO 2006/041307 describes a hot tap clamp for use in establishing a branching point in an existing pipeline, to allow a new pipeline to be connected to the existing network. The clamp has two parts with means for fastening the parts around a section of a pipeline. There is a pipe socket integrated with and extending outwardly from one of the clamp parts. The proximal end of the pipe socket extends through the clamp part so that it abuts the surface of the pipeline when the clamp is mounted thereon. Welding equipment may then be passed into the pipe socket and used to create an internal weld, thereby sealing the pipe socket to the existing pipeline. The welding equipment is then replaced with milling equipment to remove the wall of the pipeline inside the weld. The pipe socket extends outwards from the clamp part at an angle of 90°, though the angle may be different.
However, this technique is only designed to allow fluids to enter the pipeline, and has not been designed to allow tool strings to be introduced into or removed from the pipeline. Accordingly, there is still a need for a method of milling through a pipeline to provide an entry point for tools to allow pipeline intervention operations to be conducted at any desired point which will provide the flow assurance needed.